The separation of many classes of compounds by selective adsorption on molecular sieves or zeolites as well as other adsorbents is well known. Also, various separations based on the degree of unsaturation are known, e.g., esters of saturated fatty acids from unsaturated fatty acids with X or Y zeolites exchanged with a selected cation from U.S. Pat. No. 4,048,205, monoethanoid fatty acids from diethanoid fatty acids with cross-linked polystyrenes, e.g., "Amberlite" from U.S. Pat. No. 4,353,838. A process for separating a mixture of triglycerides, based on the iodine values, is shown in U.S. Pat. Nos. 4,277,412 and 4,284,580 in which permutite and aluminated silica gel adsorbents, respectively, can be used. The refining of oils by admixing them with magnesium silicate to adsorb coloring matter and free fatty acids from glyceride oils is disclosed in U.S. Pat. No. 2,639,289.
The adsorption properties of certain aluminophosphates have been reported. Choudhary et al, in the Journal of Catalysis, Vol. III, pp 23-40 (1988) discussed the adsorption of several alcohols and hydrocarbons on AIPO.sub.4 -5. Studies of the adsorption equilibrium of hydrocarbons, some N-compounds and water on AIPO.sub.4 -5 were reported by Stach et al in Stud. Surf. Sci. Catal., Vol. 28, (New Dev. Zeolite Sci. Techn.) pp 539-546 (1986) and by Dworezkov et al in an article entitled Adsorptive Properties of Aluminumphosphate Molecular Sieves in Adsorption and Catalysis on Oxide Surfaces (Che and Bond Editors) pp 163-172 (1985). None of the above suggest the separation of fatty acids and triglycerides.
The synthesis and properties of the AIPO.sub.4 series of aluminophosphate zeolites concerned here are set forth in U.S. Pat. No. 4,310,440 (AIPO.sub.4 -11) and Wu et al, Nature, Vol. 346, Aug. 9, 1990, pp 550-2, and Davis et al, Nature, Vol. 331 (1988) pp 698-9 (VPI-5 sometimes referred to herein as AIPO.sub.4 -54), respectively, which are incorporated herein by reference.
The invention herein can be practiced in fixed or moving adsorbent bed systems, but the preferred system for this separation is a countercurrent simulated moving bed system, such as described in Broughton U.S. Pat. No. 2,985,589, incorporated herein by reference. Cyclic advancement of the input and output streams can be accomplished by a manifolding system, which are also known, e.g., by rotary disc valves shown in U.S. Pat. Nos. 3,040,777 and 3,422,848. Equipment utilizing these principles are familiar, in sizes ranging from pilot plant scale (deRosset U.S. Pat. No. 3,706,812) to commercial scale in flow rates from a few cc per hour to many thousands of gallons per hour.
The functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components are well known, but for reference thereto, Zinnen et al U.S. Pat. No. 4,642,397 is incorporated herein.
I have found adsorbents, which, in combination with certain desorbent liquids, will selectively adsorb all the fatty acids contained in various triglyceride/fatty acid feed materials; the triglycerides are relatively non-adsorbed and elute as a class near the void. Thus, the triglyceride components of the feed are eluted as raffinate and the fatty acids are adsorbed and eluted as extract by desorption with the desorbent. For feed material containing major amounts of triglycerides, this so-called rejective separation of the major component is desirable since utilities are lower and adsorbent capacity for the adsorbed components, is lower per unit of output product.
These desorbents are thermally stable and thus can be regenerated easily at elevated temperatures without collapsing the pore structure. Furthermore, since there are no metal exchange ions, they are deemed suitable for the separation of food products.
I have discovered a method for separating fatty acids, including mixtures of unsaturated and saturated fatty acids, as a class, from triglycerides. The triglycerides also may be a mixture of triglycerides, including saturated, monounsaturated and polyunsaturated.